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Topic: Need help with reaction  (Read 3808 times)

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Offline LocGMD

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Need help with reaction
« on: January 21, 2016, 09:42:52 PM »
I'm starting with 1,6 dibromohexane and I need to find a way to get to a 1,6 hexanediol
I was thinking of adding a sort of OH base to undergo a substitution reaction
« Last Edit: January 21, 2016, 11:07:49 PM by LocGMD »

Offline TheUnassuming

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Re: Need help with reaction
« Reply #1 on: January 22, 2016, 03:30:54 PM »
Did you just cover SN2 in class?
When in doubt, avoid the Stille coupling.

Offline Babcock_Hall

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Re: Need help with reaction
« Reply #2 on: January 22, 2016, 06:27:07 PM »
Can you clarify what you mean by a sort of OH base?

Offline LocGMD

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Re: Need help with reaction
« Reply #3 on: January 23, 2016, 12:17:19 AM »
Can you clarify what you mean by a sort of OH base?
Well I was thinking about using water to get my desired product or a base like NaOH since I need to achieve the 1,6 alcohol subs. I'm trying my best to understand Sn2 in class but I just need a little help with this one issue. Any help is much appreciated   :D

Offline Babcock_Hall

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Re: Need help with reaction
« Reply #4 on: January 23, 2016, 10:32:14 AM »
If we are choosing between water and hydroxide ion (OH)1-, which is the stronger nucleophile, and why?

Offline zarhym

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Re: Need help with reaction
« Reply #5 on: January 31, 2016, 11:13:56 PM »
You can add 2.5 eq n-buLi and stir the mixture for a while. And then, dump everything into water.

This will be a fun reaction.
When you are doing this, try stay safe. 

Offline orgopete

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Re: Need help with reaction
« Reply #6 on: February 01, 2016, 09:03:37 AM »
You can add 2.5 eq n-buLi and stir the mixture for a while. And then, dump everything into water.


I'm skeptical that this will give the desired diol (though it could if ...). Please show the mechanism.
Author of a multi-tiered example based workbook for learning organic chemistry mechanisms.

Offline Babcock_Hall

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Re: Need help with reaction
« Reply #7 on: February 01, 2016, 09:12:44 AM »
If solubility of NaOH is a problem, there are ways around this in theory.  I don't have direct experience, however.

Offline zarhym

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Re: Need help with reaction
« Reply #8 on: February 01, 2016, 09:48:17 AM »
You can add 2.5 eq n-buLi and stir the mixture for a while. And then, dump everything into water.


I'm skeptical that this will give the desired diol (though it could if ...). Please show the mechanism.

NVM, I was wrong. The cold whether decreases the momentum of my mind.
If you do as what I just said, the reaction goes the other way. And you will end up having hexane, not diol.

However, you use 1,4-dibromobutane and t-BuLi mixture to have the lithium halogen exchange, then react with excess amount of Formyl chloride, you should end up having dialdehyde. And you can reduce this to diol.

---------------------------The reaction above will be highly exothermic, even explosive.----------------------------------------------

« Last Edit: February 01, 2016, 11:34:27 AM by zarhym »

Offline TheUnassuming

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Re: Need help with reaction
« Reply #9 on: February 01, 2016, 12:49:25 PM »
Do you think the Li-X exchange will happen faster (consistently enough for high yield) than deprotonation/elimination, or Li-X on one end which cyclizes on the other bromide? 

I know in some cases Li-X exchange can happen faster than deprotonation events, but I wonder if it would preferentially form the di-lithiated species or go down a different pathway. 

Given the cheapness of the material, to get oxidative dehalogenation I would probably just hit it with a hydroxide source and assume some loss to the elimination pathway.   If it was a more precious material, you could use an Ag+ source as well... but that seems like over kill on such a simple substrate... and probably overkill for the OP's sophomore organic chemistry class for that matter :P.
When in doubt, avoid the Stille coupling.

Offline Babcock_Hall

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Re: Need help with reaction
« Reply #10 on: February 01, 2016, 04:05:15 PM »
@OP,

How would you choose conditions to maximize the substitution products over the elimination products?

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